1. Field of the Invention
The present invention relates to an ophthalmological apparatus, such as a digital fundus camera, for taking photographic images of an eye to be examined in ophthalmological clinics, etc.
2. Description of the Related Art
FIG. 4 is a block diagram of the construction of a typical digital fundus camera. Inside a fundus camera 1, an objective lens 2 and a perforated mirror 3 are disposed along the optical path in front of an eye E to be examined, an observation photographing optical system 4 is disposed in the direction of transmittance through the perforated mirror 3, and an illumination optical system 5 is disposed in the direction of the incidence of the perforated mirror 3. These optical systems each include an illumination light source, and a power supply 11 is provided therefor. In the rear of the observation photographing optical system 4, an image pickup device 6, composed of two-dimensional image pickup elements, is mounted. The image pickup device 6 is connected to a video amplifier 7, a converter 8, and an image storage device 9 in that order. A controller 10 controls the entire system.
With such a construction, a light beam from a halogen lamp light source of the fundus illumination optical system 5 is projected from below the perforated mirror 3. Then, the light beam is reflected to the left in a portion peripheral to the perforated mirror 3, passes through the objective lens 2, and irradiates the fundus Er of the eye E to be examined. The light beam reflected from the fundus Er passes through the objective lens 2, and passes, to the right, through the opening in the center of the perforated mirror 3. Focusing adjustment is performed thereon in the observation photographing optical system 4, and the light beam is formed into an image in the imaging plane of the image pickup device 6. The image pickup device 6 outputs an analog video signal, and amplification, clamping, and band limitation are performed on the analog video signal in the video amplifier 7. In the converter 8, the analog video signal is converted into digital image data, and this image data is stored in the image storage device 9. The power supply 11 is a power supply for the illumination light source.
A photographer performs alignment between the eye E to be examined and the optical system, and presses a photographing switch. Thereupon, a strobe light source for taking pictures, disposed in the fundus illumination optical system 5, emits light as a result of a predetermined timing between the image pickup device 6 and a video cycle being taken. Then, the power supply 11 starts charging immediately after the strobe light emission. The light beam from the strobe light source illuminates the fundus Er of the eye E to be examined in a manner similar to the above-mentioned observation light, and the light reflected from the fundus Er is captured by the image pickup device 6 in a similar manner. This is stored as a fundus image signal and is output as an image signal at the next video cycle. This video signal is converted into digital data by the converter 8, such as an A/D converter, is stored in the image storage device 9, and is displayed or stored.
However, during the period in which the image picked up by the image pickup device 6 is output, that is, during the period in which the converter 8 performs the conversion operation, there is a possibility that high-frequency noise occurring due to the operation in the image storage device 9, the power supply 11, etc., enters the signal system and the ground line of the converter 8, exerting an adverse influence on digital conversion. In particular, during control for controlling large amounts of power, much noise occurs. In the converter 8, since a video signal is digitally converted at 8 to 10 bits, if the analog signal is assumed to be at 1 V at the peak-point voltage, a very small voltage of 0.97 to 3.9 mV per bit must be handled. At this time, since the accuracy is {fraction (1/2 )} bits, it is necessary to reduce noise to less than half of this voltage. In particular, in the photographing of the fundus, since the original S/N ratio of the image is not good, the problem of noise cannot be ignored. In the fundus image which is greatly affected by noise, noise may become an obstacle to accurately performing examination of very small blood vessels and the optic nerve.
An object of the present invention is to provide an ophthalmological apparatus which solves the above-described problems and which is capable of taking high-quality pictures by preventing the occurrence of noise or by reducing noise.
According to one aspect, the present invention that achieves at least one of these objectives relates to an ophthalmological apparatus comprising an illuminator configured and positioned to project light toward an eye to be examined, thereby illuminating the eye to be examined. The apparatus also comprises an image pickup device configured and positioned to receive light from the illuminated, examined eye, to form an image of the illuminated, examined eye, and to generate a signal representing the image. The apparatus further comprises a signal converter, connected to the image pickup device to receive the signal generated by the image pickup device. The signal converter is configured to convert the received signal to digital data by a conversion operation. The apparatus also includes at least one additional element, and a controller, connected to the illuminator, the image pickup device, the signal converter, and the at least one additional element. The controller receives signals from image pickup device, the signal converter, and the at least one additional element. The controller transmits control signals to the illuminator, the image pickup device, the signal converter, and the one additional element, respectively controlling the illuminator, the image pickup device, the signal converter, and the at least one additional element. The controller also generates a limit signal to limit a predetermined operation of at least one of the illuminator and the at least one additional element while the signal converter is performing a conversion operation.
According to another aspect, the present invention that achieves at least one of these objectives relates to an ophthalmological apparatus comprising illuminating means for illuminating an eye to be examined, imaging means for forming an image of the illuminated eye and for generating a signal representing the image, converting means for converting the signal to digital data by a conversion operation, at least one additional means for performing an additional function, and control means for controlling the illuminating means, the imaging means, the converting means, and the at least one additional means and for limiting a predetermined operation of at least one of the illuminating means and the at least one additional means while the signal converting means is performing the conversion operation.
According to still another aspect, the present invention that achieves at least one of these objectives relates to a method of examining the eye comprising the steps of illuminating an eye to be examined, forming an image of the illuminated eye and for generating a signal representing the image, converting the signal to digital data by a conversion operation, the digital data containing information to enable an examiner to examine the eye, performing an additional operation in examining the eye, and limiting a predetermined operation of at least one of the illuminating step and the performing step while the signal converting step is performing the conversion operation to reduce noise generated during the at least one of the illuminating step and the performing step.
According to still another aspect, the present invention that achieves at least one of these objectives relates to a noise reducing device for an ophthalmological apparatus comprising an illuminator configured and positioned to project light toward an eye to be examined, thereby illuminating the eye to be examined, an image pickup device configured and positioned to receive light from the illuminated, examined eye, to form an image of the illuminated, examined eye, and to generate a signal representing the image, a signal converter, connected to the image pickup device to receive the signal generated by the image pickup device, the signal converter being configured to convert the received signal to digital data by a conversion operation, and at least one additional element. The noise reducing device comprises a controller, connected to the illuminator, the image pickup device, the signal converter, and the at least one additional element. The controller receives signals from the image pickup device, the signal converter, and the at least one additional element. The controller also transmits control signals to the illuminator, the image pickup device, the signal converter, and the one additional element, respectively controlling the illuminator, the image pickup device, the signal converter, and the at least one additional element. In addition, the controller generates a limit signal to limit a predetermined operation of at least one of the illuminator and the one additional element while the signal converter is performing a conversion operation.
According to still another aspect, the present invention that achieves at least one of these objectives relates to a method of reducing noise produced during an eye examination with an ophthalmological apparatus that illuminates the eye to be examined, forms an image of the illuminated, examined eye, and generates a signal representing the image, converts the signal to digital data by a conversion operation, and performs at least one additional process with at least one additional element. The noise reducing method comprises the steps of limiting a predetermined operation of at least one of the illuminating operation and the performing of at least one additional process by the ophthalmological apparatus step while the ophthalmological apparatus converts the signal to digital data, thereby reducing noise generated during at least one of the illuminating operation and the performing of at least one additional process.
The above and further objects, aspects and novel features of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.